No response to m105 command

My MakerGear M2 has suddenly decided to stop responding to commands. It does the normal reset when you start the connection but then the firmware never seems to respond after sending back the SD card status is okay. Sending a M105 command generates no response and no more led flashes on the TX side. I see Rx led flash each time I send a command but no response after the initial reset. What could cause the Marlin firmware to stop responding at this point? Is there any way to get more debug info out of it?

Connecting...
start
Printer is now online.
echo: External Reset
Marlin 1.0.0
Using tool 0.
echo: Last Updated: Apr 26 2015 20:59:26 | Author: (none, default config)
Compiled: Apr 26 2015
echo: Free Memory: 4141 PlannerBufferBytes: 1232
echo:Hardcoded Default Settings Loaded
echoteps per unit:
echo: M92 X88.88 Y88.88 Z400.00 E471.50
echo:Maximum feedrates (mm/s):
echo: M203 X500.00 Y500.00 Z25.00 E25.00
echo:Maximum Acceleration (mm/s2):
echo: M201 X4000 Y4000 Z100 E10000
echo:Acceleration: S=acceleration, T=retract acceleration
echo: M204 S2000.00 T3000.00
echo:Advanced variables: S=Min feedrate (mm/s), T=Min travel feedrate (mm/s), B=minimum segment time (ms), X=maximum XY jerk (mm/s), Z=maximum Z jerk (mm/s), E=maximum E jerk (mm/s)
echo: M205 S0.00 T0.00 B20000 X8.00 Z0.40 E5.00
echo:Home offset (mm):
echo: M206 X0.00 Y0.00 Z0.00
echoID settings:
echo: M301 P25.89 I1.94 D86.53
echoD card ok
SENDING:M105
SENDING:M105
SENDING:M105

You are on a very old version of Marlin. A lot of improvements have been made to the SD Memory card stuff. Can you re-format your memory card and see if it still has problems?

But either way, you really should load up RCBugFix. I think you will be impressed with it.

I probably should have changed the title of my initial post because it doesn't respond to any command after the init reset. No response to the jog commands or home commands in Pronterface.

Cura doesn't work either. After the initial connect when the fans shut off and then restart, I get no response from the printer. Cura's log says ...

Listening for engine communications on 49674
Closing down

I'm not familiar with RCBugFix, is that a branch of the Marlin firmware? Is it likely to give me any diagnostic information?

Right now my suspicion is that something has gone wrong with the Rambo board that makes the current firmware fall over. The firmware is old but had been working fine for nearly 2 years so I'm not sure how updating the firmware would help unless it has additional status reporting that can tell me why it is crashing?

RCBugFix is the most correct version of the Release Candidate we are working with. It is here: [github.com]

If your electronics is bad, it doesn't make sense to be debugging firmware on it. I suspect you are going to get different (and better) results if you bring up RCBugFix. And there is extensive debugging built into it. If you get it up and running, this problem won't be difficult to resolve because we just turn on the debugging feature and see exactly what it thinks about everything and the decisions it makes.